The physiological response to steroid hormones is mediated by specific interaction of steroids with nuclear receptors, which are ligand-activated transcription factors that regulate the expression of target genes. These receptors consist (in an amino-terminal-to-carboxy-terminal direction) of a hypervariable amino-terminal domain that contributes to the transactivation function; a highly conserved DNA-binding domain responsible for receptor dimerization and specific DNA binding; and a carboxy-terminal domain involved in ligand binding, nuclear localization, and ligand-dependent transactivation.
In vivo, estrogen has been identified as having utility in treating adverse behavioral/clinical symptoms that accompany fluctuations in hormones associated with menopause in aging women, although the biochemical basis for these effects has never been determined. As such, the treatment of behavioral effects with estrogen in human subjects has been restricted to the treatment of menopause in women who demonstrate signs of deficiency in estrogen, and use in prevention of the sequelae of menopause, namely hot flashes and osteoporosis, which are typically corrected by replacement therapy of estrogen.
Recently, cDNA was cloned from rat prostate and shown to have significant homology to a previously isolated rat estrogen receptor (Kuiper et al., Proc. Natl. Acad. Sci. USA 93:5925, 1996); this receptor was designated ERβ to distinguish it from the previously cloned receptor, ERα, Rat ERβ was shown to be expressed in prostate, testes, ovary, and thymus, in contrast to ERα, which is most highly expressed in uterus, breast, liver, and pituitary. A human ERβ homologue has been reported (Mosselman et al., FEBS Letts. 392:49, 1996), having the amino-terminal sequence Gly-Tyr-Ser. A human ERβ has been described in PCT Publication WO 99/07847.
Hepatic lipase (HL) is a lipolytic enzyme that is synthesized primarily in the liver. HL hydrolyzes triglycerides and phospholipids present in chylomicron remnants, intermediate density lipoprotein (IDL), and high-density lipoprotein (HDL). Through its function as a lipolytic enzyme, HL plays a major role in the metabolism of circulating plasma lipoproteins resulting in elevation of small, dense atherogenic LDL with a decrease in HDL plasma levels. Several lines of evidence demonstrate the important role of HL in HDL metabolism. Patients with a genetic deficiency of HL have increased plasma levels of HDL cholesterol and phospholipids (Breckenridge et al, Atherosclerosis, 45:161, 1982). Increased HDL is also a hallmark of HL-deficient states induced by infusion of anti-HL antibodies (Goldberg et al., J. Clin. Invest. 70:1184, 1982), genetic manipulation (Homanics et al. J. Biol. Chem. 270:2974, 1995) or naturally present in various animal models (Clay et al. Biochim. Biophys. Acta. 1002:173, 1989). Conversely, overexpression of HL decreases plasma HDL concentrations in transgenic mice (Busch et al. J. Biol. Chem. 269:16376, 1994) and rabbits (Fan et al. Proc. Natl. Acad. Sci. USA 91:8724, 1994).
In terms of ERT in postmenopausal women, it is well established that trafficking of lipoprotein cholesterol is enhanced via the reverse cholesterol transport system. HL activity has been shown to be reduced by 31% due to ERT, levels similar to that found in premenopausal women (Tikkanen et al. Acta Obstet Gynecol Scand Suppl. 88:83, 1979). Diminishment of HL activity by ERT is thought to improve the reverse cholesterol transport system by blocking the metabolism of HDL thereby maintaining higher plasma levels of HDL. In addition, inhibition of HL activity may result in a reduction in the amount of small, dense atherogenic LDL.
Thus, there is a need in the art to identify compounds that can modulate HL production. There is a further need in the art to identify compounds that can act through the estrogen receptor to modulate, and preferably inhibit, HL expression by acting on the HL promoter.